1. Field of the Invention
The present invention relates to a front end module used in a mobile communication device.
2. Description of the Related Art
The front end module (FEM) is a transmitting/receiving device used in a mobile communication device to control an electric wave signal. The FEM is a complex component on which a plurality of electronic components is mounted in a single substrate.
For example, a conventional FEM for processing a code division multiple access (CDMA) will now be described.
FIG. 1 is a circuit block diagram of a conventional CDMA FED.
Referring to FIG. 1, a conventional CDMA FEM includes a duplexer 20, a receiver 30, and a transmitter 40. The transmitter 40 includes a transmitting process module 46 (a Tx BBA or RF transmitter), transmitting filter 44, and a power amplifier module (PAM) 42. The receiver 30 includes a low noise amplifier (LNA) 32, a receiving filter 34, and an receiving process module 36 (Rx BBA or RF receiver).
The duplexer 20 separates receiving and transmitting signals and transmits the same to an antenna 10 or a receiver 30. The receiving process module 36 and a transmitting process module 46 are connected to a base band process unit 50.
The base band process unit 50 generates multimedia data by analyzing a digital signal to control each circuit unit.
The transmitting process module 46 and the receiving process module 36 modulate or demodulate an intermediate frequency signal or a digital signal and perform an analog/digital (A/D) or D/A converting process.
The transmitter filter 44 or the receiver filter 34 filters off a transmitting band frequency signal or a receiving band frequency signal. The PAM 42 and the LNA 32 amplify the transmitted signal so that the transmitted signal can be processed as the transmitting or receiving signal.
The CDMA FEM is generally mounted on a multi-layered structure substrate. The circuit devices are surface-mounted and die-bonded on a top layer and a ground pattern, a wire pattern, and the like are formed on an interlayer. In addition, a ground pattern, a terminal pattern, and the like are formed on a bottom layer. The layers are electrically conducted through a via-hole.
Problems of the convention FEM will now be described hereinafter.
First, the conventional FEM has the following structure problems of the substrate.
Since most of the regions of the substrate are opened, when the FEM is mounted through a surface mounting technology, the FEM may be sided and thus the performance of the FEM varies according to an amount of solder member deposited for the electron conduction.
In addition, the conventional FEM is comprised of a variety of electronic components and a barrier is formed to prevent electric wave interference and disperse heat. A shield formed of metal is provided to correspond to the barrier. However, there is a limitation in preventing the electric wave interference between devices using the barrier.
Furthermore, since the components of the FEM are grouped in many blocks and mounted. Therefore, the mounting, bonding, and molding processes must be independently performed. Therefore, the overall process is complicated and the process treating time increases. In addition, in the conventional CDMA FEM, a chip inductor (not shown) is generally used as an antenna terminal of the duplexer 20. However, the chip inductor is relatively expensive and requires a space for the surface mounting. In addition, the receiving performance may vary according to the change during the surface mounting process.
In addition, since the conventional FEM uses a plurality of electric wave paths using a plurality of receiving components such as receiving chips, it can realize the diversity technology that can increase the number of communication channels. In this case, since the number of the receiving chips and the peripheral components increases, the mounting area of the substrate must be enlarged. This makes it difficult minimize the mobile communication device in which a multi chip module (MCM) is mounted.
Second, the conventional FEM has a variety of problems in the overall operational function.
In the conventional FED, a switching circuit unit (not shown) is connected to the PAM 42 to control the operation of the PAM 42. According to this power supply structure using the switching circuit unit (not shown), since a relatively high intensity of signal is applied, the PAM 42 may be damaged. Furthermore, a noise component is inputted together with electric power, the performance of the PAM 42 may be unstable.
Furthermore, when the circuit devices constituting the conventional FEM are mounted on the substrate, the transmitting and receiving performance may vary. That is, according to the arrangement design of the receiving filter 34, the receiving sensitivity, intermodulation distortion property, single tone desensitization property, and the like may vary. The performance value of the convention FEM is required to be improved.
Furthermore, as the mobile communication device is small-sized and lightweight, the PAM 42 and the duplexer 20 of the conventional FEM are coupled at a complex module. By the complexion of the device modules, the impedance tuning area of the final product is reduced.
That is, the conventional complex module is designed to conform to the efficiency and impedance appropriate for the linearity and the performance of the complex module displays its proper performance only for 50Ω terminal impedance of the antenna. Therefore, when the performance improvement for certain terminal impedance is done by adjusting an impedance of a bonding portion in the device, it is impossible to realize the performance improvement in the convention complex module. In addition, since the PAM 42 has a matching circuit unit inside thereof and another matching circuit unit needs to be provided between the PAM 42 and the duplexer 20, a proper space and additional matching devices are required.
In the conventional CDMA mobile communication device, when the RF signal is converted into an intermediate frequency signal, a reference frequency signal transmitted from a voltage controlled oscillator (VCO) (not shown) is necessary. However, when the VCO is designed in a single module according to the prior art, phase noise may be mixed, thereby deteriorating the performance of the receiving unit.